Lecturing in the U.S. Dutchborn Professor Dirk Struik is according to the FBI an active and dedicated Communist. A nationwide fund-raising campaign began in his defense.

Except for a scattering of top-level mathematicians across the nation, and the students in his classes at M.I.T., few Americans had ever heard of Dirk J. Struik when his name first appeared in the news two years ago. He was a mousy-looking mathematician who had come to the U.S. from…